JWST surpasses, enhances Hubble’s deepest image ever

There’s a recipe to seeing farther back in time than ever before.

The blank region of sky, shown in the yellow L-shaped box, was the region chosen to be the observing location of the original Hubble Deep Field image. With no known stars or galaxies within it, in a region devoid of gas, dust, or known matter of any type, this was the ideal location to stare into the abyss of the empty Universe. Today, we know of even more pristine regions than we did in the early 1990s.

First: point your telescope at an empty patch of sky, observing for as long as you dare.

Only because the most distant galaxy spotted by Hubble, GN-z11, is located in a region where the intergalactic medium is mostly reionized, was Hubble able to reveal it to us at the present time, breaking the prior record held by EGSY8p7. Other galaxies that are at this same distance but aren’t along a serendipitously greater-than-average line of sight as far as reionization goes can only be revealed at longer wavelengths, and by observatories such as JWST. At present, GN-z11 has been relegated to the 9th most distant galaxy known as of 2024: in the JWST era.

Choose a clear line-of-sight: possessing minimal light-blocking material.

The transmittance or opacity of the electromagnetic spectrum through the atmosphere. Note all the absorption features in gamma rays, X-rays, and the infrared, which is why the greatest of our observatories in these wavelengths are all located in space. The infrared, in particular, was spectacularly covered by NASA’s Spitzer, and is presently covered by NASA’s JWST.

Use a space-based telescope, avoiding Earth’s absorptive, distorting atmosphere.

Whenever a galaxy emits light, the light that’s eventually seen by the observer who receives it will have a different set of properties and wavelengths than when that light was first emitted, owing to two properties: the relative motion of the light source to the observer, as well as the expansion of the Universe that occurs between the source and observer. The greater the distance to the galaxy, the greater the observed redshift, and also the greater the amount of observed time dilation, as the signal the observer receives will be “stretched out” over time as well.

And observe at long wavelengths, compensating for cosmic redshift.

This is the final result of the full, 23 day observations of the Hubble eXtreme Deep Field team. In this tiny region of the sky, which consists of many regions of serendipitously little light-blocking material, some of the deepest objects ever seen are located. But with less than 1 day of observations in the same region, JWST can already reveal galaxies that Hubble could not.

Before JWST, the Hubble eXtreme Deep Field recorded our deepest views.

Over the course of 50 days, with a total of over 2 million seconds of total observing time (the equivalent of 23 complete days), the Hubble eXtreme Deep Field (XDF) was constructed from a portion of the prior Hubble Ultra Deep Field image. Combining light from ultraviolet through visible light and out to Hubble’s near-infrared limit, the XDF represents humanity’s deepest view of the cosmos: a record that stood until the JWST’s first deep field was released on July 11, 2022.

With 23 days of multi-wavelength observations, it unveiled unprecedented riches.

The full Moon takes up approximately 0.2 square degrees on the sky, meaning that approximately five of them are required to fill one square degree of space. The Hubble eXtreme Deep Field, however, is much smaller, and it would take approximately 776 of them to cover one square degree on the sky. That tiny region of sky had 5500 galaxies within it, despite covering just 1-32,000,000th of the sky.

Seeing ~5,500 galaxies in just 1/32,000,000th of the sky, it revealed galaxies ~400 million years post-Big Bang.

The JWST, now fully operational, has seven times the light-gathering power of Hubble and is able to see much farther into the infrared portion of the spectrum, revealing those galaxies existing even earlier than what Hubble could ever see, owing to its longer-wavelength capabilities and much lower operating temperatures. Compared with other near-IR and mid-IR observatories, JWST’s capabilities are a factor of 10-1000 better, enabling superior discoveries.

But JWST is larger, sharper, and reaches much longer wavelengths.

This animation showcases a portion of the Hubble eXtreme Deep Field, with 23 days of cumulative data, and a simulated view of what scientists expected JWST might see when it viewed this region. This simulation predates JWST’s launch, and has since been spectacularly superseded by actual JWST data.

With only 20 hours of observing time in the same field-of-view, it’s already revealed what Hubble can’t.

This animation switches points of view between the Hubble Ultra Deep Field and the JWST view of an overlapping region of space. Because of the difference in telescope size and resolution, the JWST views are downsampled by about a factor of 4 in resolution to make these two images match.

Ionized galactic gas shines bright in JWST’s infrared views.

This region of space, viewed first iconically by Hubble and later by JWST, shows an animation that switches between the two. Both images still have fundamental limitations, as they were acquired from within our inner Solar System, where the presence of zodiacal light influences the noise floor of our instruments, and cannot easily be removed. The extra presence of point-like red objects in JWST images, also known as “little red dots,” has finally been explained, but other puzzles still remain.

Foreground stars are resolvable into binaries.

Preliminary total system throughput for each NIRCam filter, including contributions from the JWST Optical Telescope Element (OTE), NIRCam optical train, dichroics, filters, and detector quantum efficiency (QE). Throughput refers to photon-to-electron conversion efficiency. By using a series of JWST filters extending to much longer wavelengths than Hubble’s limit (between 1.6 and 2.0 microns), JWST can reveal details that are completely invisible to Hubble. The more filters that are leveraged in a single image, the greater the amount of details and features that can be revealed.

But most remarkable are objects visible to JWST, but unseen by Hubble.

Because of the shape of its NIRCam imager’s field-of-view, whenever you look at a specific region of the sky with JWST’s NIRCam instrument, you automatically get to image a similarly-sized field-of-view with equal resolution that’s about an arc-minute away from the original. This field, just a bit out-of-frame (to the right) of the Hubble Ultra Deep Field’s full extent, offers some fascinating “Bonus science” to JWST enthusiasts.

All across this high-resolution JWST deep-field, new objects emerge.

Overlapping almost 100% with the Hubble eXtreme Deep Field, this JWST view shows, with just 20 hours of observations, many details and perhaps hundreds of objects that are too faint and red to be seen even with 23 days worth of Hubble Space Telescope views.

Some are faint, dusty foreground objects.

This section of one of our deepest views of the Universe, acquired with JWST, overlaps with data from the Hubble eXtreme Deep Field. Compared to Hubble, JWST reveals an enormous number of objects previously invisible to Hubble, even with only ~4% of the observing time. Most of these galaxies are small and low-mass, but are forming stars rapidly right now, enabling JWST to reveal their presence.

But others will be ultra-distant galaxies: well beyond Hubble’s limited vision.

A portion of a JWST deep-field image, shown with the Hubble observations as its counterpart. Within the JWST field are a significant number of objects not seen by Hubble, showcasing JWST’s ability to reveal what Hubble could not, thanks predominantly to its longer-wavelength capabilities. All of the light produced by stars, black holes, and excited atoms contributes to the cosmic optical background, but excess light beyond that would present a cosmic puzzle.

JWST’s sharper, longer-wavelength views are revealing the deepest objects of all-time.

This portion of the newest JWST image that covered part of Hubble’s ultra-deep field reveals a number of distant galaxies, highlighted manually, that are present in the brief JWST views but not in the long-exposure Hubble views. Some of these may indeed be cosmic record-breakers.

Spectroscopic studies, upcoming, will shatter even JWST’s current cosmic record.

The spectroscopic identification of the Lyman break signature, present and easily visible in all four ultra-distant, JWST-identified galaxies from the JADES deep field, confirms their redshift and distance. This observation gave us, at the time, the top three most distant galaxies of all, with spectroscopic confirmation. The Lyman break feature, normally resulting in an ultraviolet photon, can be seen well into the infrared from these galaxies owing to the redshifting of the light during its journey.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.